The present invention relates to a method and apparatus for determining whether an intubated patient has been properly intubated.
There have been numerous techniques developed for detecting accidental esophageal intubation (see Pat. Nos. 4,879,999, 4,572,208, 4,728,499, 5,166,075, 5,179,002, 5,648,451, 5,749,358, 4,928,687, 5,156,159, and 2,136,236). For the most part, these patents deal with devices and methods for indicating proper placement of an endotracheal tube by detecting (colorimetry) the presence of carbon dioxide in expired air passing through the device. If the patient has ingested a carbonated beverage prior to intubation, esophageal CO.sub.2 may be present and cause misleading indication of the position of the tube.
The present invention determines whether or not an intubated patient has been properly intubated (i.e., whether the tube is in the trachea or incorrectly in the esophagus) by measuring the .DELTA..rho.O.sub.2 between the inspired and expired gases.
When breathing air, a person uses about one quarter of the oxygen he or she inspires. When breathing oxygen enriched gas they use a correspondingly smaller percentage, but there is still a substantial signal to work with. Rather than just measure the absolute difference in the level of oxygen, between inspired and expired, it would be preferable to measure the derivative, i.e. the differential d.rho.O.sub.2 /dt, and more preferable, the second derivative, i.e. change in slope instead of, or in addition to, the absolute difference in oxygen content. However, it should be understood that this is not a limiting feature on the broad aspects of the invention.
The measurement(s) will be displayed on a visual display or by an audible annunciator or by both. The display could comprise one LED illuminating at the inflection point when the slope changes positively and a second LED illuminating at the inflection point when the slope changes negatively, thereby obtaining a breath-to-breath indication. Additional measurements may also be made, as already mentioned, of the absolute level (tension or partial pressure) of the inhaled and exhaled gas in order to provide additional information which may be needed to reliably determine whether oxygen is being used by the patient. These measurements may be necessary, particularly during transient conditions, should oxygen be added to the inspired gas.
Thus, the objective of the invention is to provide an improved method and apparatus for determining whether an intubated patient has been properly intubated.